Looking after solar thermal hot water systems

Two collector in-roof Grant Solar Thermal System installation

It is well known that solar thermal systems are low maintenance, especially when compared to other types of heating systems such as gas or oil. However, basic maintenance is recommended to help a solar thermal hot water system work efficiently and trouble-free. In this blog we cover some of the steps that should be carried out annually to maintain a solar thermal system.

How to maintain a solar thermal system

Grant’s Solar Thermal Systems are popular with homeowners for several reasons. Firstly, the systems harness free energy from the sun and utilise this to heat water. Secondly, a solar thermal system can significantly reduce a household’s fuel bill. And thirdly, minimal intervention is needed when it comes to servicing and maintaining because solar thermal maintenance is simple.

The Grant Sahara collector has 4mm self-cleaning glass which helps the system maintain itself but there are some annual servicing procedures that installers can complete to further aid the efficient operation of a solar thermal hot water system.

Take a look at the key checks below.

Essential system checks

There are a number of components within the system that installers need to check as part of solar thermal system service: 

  • Collectors - assess their fitting and condition including the glass, pipe connections and collector sensor
  • System Pipework - assess the PRV operation and expansion vessel

With the collectors, the fixings should be secure and, if necessary, retightened. The condition of the collectors should also be reviewed – checks should be carried out to ensure that the glazing is undamaged and the glass should be cleaned to remove any dirt deposits. Turning to the pipe connections, these should be checked for any evidence of leaks and with the pipe insulation, installers should look at any exposed pipes and if damaged insulation is found, this should be replaced. The final thing to assess with the collectors is the collector sensor which should be correctly located and securely fitted.

The next place to turn to is the system pipework. The system should be visually inspected to look for any leaks and, if found, these should be resolved. The Pressure Reducing Valves (PRV) operation should be tested by briefly rotating the plastic cap on the valve to operate. The condition of pipe insulation here should also be checked with any damaged sections replaced, if required.

The pressure in the expansion vessel should also be monitored and this can be completed in four simple steps which are outlined below:

  1. Close the isolation valve on the expansion vessel connection
  2. Open the small drain cock on the connector and drain off a small amount of solar fluid into a clean container (keep this aside to test, please see below)
  3. Check the air charge in the vessel
  4. Adjust or re-pressurise the vessel as necessary to achieve the correct pressure (this may require putting additional solar fluid into the system)

Greater detail is provided within the Solar Thermal Installation Manual (DOC 0073).

Testing the solar fluid

As mentioned above, when testing the expansion vessel pressure, a small amount of solar fluid should be extracted so that a couple of tests can be carried out. Using a refractometer, the first test is to check the antifreeze concentration and level of protection.

Secondly, using suitable litmus indicator strips, the acidity ph value should be tested. If either of these tests indicate the fluid is unsuitable, the solar fluid in the system should be replaced.

Restarting the system

After carrying out the system checks and testing the solar fluid, it is also recommended to check the hot water storage cylinder that the solar thermal system feeds into. The cylinder should be serviced in full accordance with the manufacturer’s recommendations – for example, Grant’s hot water cylinders should be serviced annually. The cylinder sensor should also be looked at to make sure it is correctly positioned and fitted securely.

Once all of the above has been completed, the system can be restarted and put back into operation.

Provided below is a summary of the steps involved in restarting a Grant Solar Thermal System – when carrying out a system restart, please have the complete manual to hand for further guidance.

  1. Check the cold system pressure, via the press gauge, and make sure it is correct for static height of the system – top up or re-fill as required
  2. After reconnecting the power supply to the controls, check that the settings on the solar controller are correct and then operate the override on the controller, checking that the solar pump starts
  3. With the solar pump running, check the volume flow rate and reset as necessary. It is important to ensure that the correct system volume flow rate is also set in the solar pump station.

As this blog has hopefully demonstrated, looking after a Grant Solar Thermal system is straightforward and simple but these basic procedures are important.

It is important to point out that the procedures detailed in this blog should be carried out by a suitably competent person, such as the installing engineer, and not the homeowner. Also, before commencing any work on a solar thermal system, the collectors should be covered and the system allowed to cool down. The electrical supply to all system controls should also be isolated.

Click here to read more about the solar thermal range from Grant UK.

Phil Stanley
Training Manager at Grant UK
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